There are surprising differences in the ease with which persons who are rated as being in excellent health and do not exhibit known circulatory defects make adjustments to certain changes in posture. Most of us are frequently altering our position from one pose to another. We arise, stand still, walk or exert ourselves in many ways without realizing that the consequent changes of bodily posture are attended with notable circulatory changes representing adjustments that make the variations in the body's position comfortable as well as physiologically effective. Not infrequently, healthy persons feel real discomfort, which may range from a vague sensation to acute dizziness or even fainting when they change from a reclining position to an upright posture. There is an evident circulatory embarrassment involved in this condition. Its nature is gradually becoming clearer as the result of careful investigation. An immediate factor that needs adjustment by the bodily mechanism